/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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/*
 * This file is available under and governed by the GNU General Public
 * License version 2 only, as published by the Free Software Foundation.
 * However, the following notice accompanied the original version of this
 * file:
 *
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/licenses/publicdomain
 */

package java.util.concurrent.locks;

/** {@collect.stats} 
 * {@description.open}
 * A synchronizer that may be exclusively owned by a thread.  This
 * class provides a basis for creating locks and related synchronizers
 * that may entail a notion of ownership.  The
 * <tt>AbstractOwnableSynchronizer</tt> class itself does not manage or
 * use this information. However, subclasses and tools may use
 * appropriately maintained values to help control and monitor access
 * and provide diagnostics.
 * {@description.close}
 *
 * @since 1.6
 * @author Doug Lea
 */
public abstract class AbstractOwnableSynchronizer
    implements java.io.Serializable {

    /** {@collect.stats}
     * {@description.open}
     * Use serial ID even though all fields transient. 
     * {@description.close}
     */
    private static final long serialVersionUID = 3737899427754241961L;

    /** {@collect.stats} 
     * {@description.open}
     * Empty constructor for use by subclasses.
     * {@description.close}
     */
    protected AbstractOwnableSynchronizer() { }

    /** {@collect.stats} 
     * {@description.open}
     * The current owner of exclusive mode synchronization.
     * {@description.close}
     */
    private transient Thread exclusiveOwnerThread;

    /** {@collect.stats} 
     * {@description.open}
     * Sets the thread that currently owns exclusive access. A
     * <tt>null</tt> argument indicates that no thread owns access.
     * This method does not otherwise impose any synchronization or
     * <tt>volatile</tt> field accesses.
     * {@description.close}
     */
    protected final void setExclusiveOwnerThread(Thread t) {
        exclusiveOwnerThread = t;
    }

    /** {@collect.stats} 
     * {@description.open}
     * Returns the thread last set by
     * <tt>setExclusiveOwnerThread</tt>, or <tt>null</tt> if never
     * set.  This method does not otherwise impose any synchronization
     * or <tt>volatile</tt> field accesses.
     * {@description.close}
     * @return the owner thread
     */
    protected final Thread getExclusiveOwnerThread() {
        return exclusiveOwnerThread;
    }
}
